The present invention relates to methods of measuring potential differences and currents, and, more particularly, the invention relates to methods of measuring the potential difference or the plasma current developed on the surface of a semiconductor wafer sample, when it is under plasma processing, during semiconductor manufacturing processes, with the semiconductor wafer located inside a plasma reactor in order to surface-treat the wafer. Also, the present invention relates to an apparatus for monitoring processes in a plasma processing apparatus by use of the measured potential difference or plasma current, and to a sample processing method that uses the process monitoring apparatus.
In general, during the manufacture of semiconductors, semiconductor wafers need to be subjected to various surface treatment processes, such as etching, and a plasma reactor that applies electromagnetic waves to generate a plasma is most commonly used as the surface processing apparatus. For such a plasma reactor, the electromagnetic waves and the plasma generate a strong electric field not only in the space of the plasma reactor, but also on the surface of the semiconductor wafer mounted on a processing table (sample mount) within the processing apparatus. When a strong electric field is generated on the surface of the semiconductor wafer, the field strength will cause a potential difference on the surface of the semiconductor wafer, and if the potential difference exceeds a predetermined value, the semiconductor wafer may be damaged. It is therefore important to measure the potential difference on the semiconductor wafer surface when processing that surface using a plasma reactor.
In this case, probing (hereinafter referred to as the first known method) is available as one of the typical methods of measuring the electric field strength and potential differences occurring inside the plasma reactor. The first known method is intended to measure the electric field strength and potential differences inside the plasma reactor by inserting conductor probes into a plasma atmosphere and, then, after scanning with the probes, detecting the voltage-current characteristics thereof.
A method of measuring the potential of a semiconductor wafer inside a plasma reactor (hereinafter referred to as the second known method) is described on page 775 of a Japanese-Version Preliminary Article Collection at the 46th Association Symposium on Applied Physics, held in the spring of 1996. For the second known method, the potential difference on the semiconductor wafer surface is measured by searching with probes embedded directly in the semiconductor wafer (which is mounted on the sample mount, namely, the semiconductor wafer mounting table, inside the plasma reactor) at a portion where the potential difference is estimated to occur, instead of searching with probes embedded in the sample mount itself.
Since the first known method, which proposes to measure the potential difference on the semiconductor wafer inside the plasma reactor, is used to detect the voltage-current characteristics of the conductor probes by scanning in a plasma atmosphere, it is necessary to transmit detection output signals from the conductor probes to an external apparatus by using connection lead wires and to provide the vacuum chambers with connection lead wire relay terminals, because the plasma is generated inside the vacuum chamber. In addition, the total structure of the plasma reactor is complex, and this makes it impossible for the potential difference on the semiconductor wafer to be measured using a simplified means.
Furthermore, since the second known method, which proposes to measure the potential difference on the semiconductor wafer inside the plasma reactor, uses probes embedded in a sample mount on which the semiconductor wafer is to be mounted, it is not only necessary for the sample mount to be of special structure, but it is also difficult to process the surface of the semiconductor wafer on this sample mount after measuring the potential difference on the semiconductor wafer by use of the sample plate. In addition, the type of sample mount to be used will differ between measurement of potential difference on the semiconductor wafer and the surface-treatment processing thereof, and this results in increased plasma reactor costs and, hence, an increased number of treatment processes.